Coloring agents are generally a powder of white or other color which is insoluble or difficultly soluble in water and organic substances, and fine wide applications as a coloring agent for ink, coating, plastic, etc. or as a functional material wherein the inherent property of coloring agents is utilized.
Coloring agents take the form of fine powder and their affinity to other substances, for example, organic polymers and organic solvents is therefore weak as compared to the cohesive force between the particles of the powder. This makes it very difficult to uniformly mix or disperse a coloring agent under ordinary mixing or dispersing conditions. Further, coloring agents tend to be reagglomerated and it is difficult to obtain a dispersion having long-term stability.
In order to solve the above problem, there were proposed a number of methods for uniformly mixing or dispersing a coloring agent with or in a solid or liquid base material by coating the surface of the coloring agent with a surfactant or a resin, or by treating said surface with a coupling agent, or by using a polymeric dispersing agent in combination.
In these methods, however, the number of process steps are larger, the operations are complicated and the effects are insufficient; thus, no satisfactory results have not yet been obtained.
Toners used for development of developing electrostatic latent images have heretofore been produced by a process which comprises dispersing, by melt-mixing, a coloring agent and other additives (e.g. static charge-controlling agent, offset-preventing agent, lubricant) in a thermoplastic resin, solidifying the dispersion, finely granulating the solid dispersion, followed by classification to obtain a product having desired particle diameters.
In order to improve the above processes for toner production by grinding, there were proposed various processes for toner production by emulsion or suspension polymerization [e.g. Japanese Patent Publication No. 10231/1961, Japanese Patent Application Kokai (Laid-Open) No. 11957/1988, Japanese Patent Application Kokai (Laid-Open) No. 266562/1987, Japanese Patent Application Kokai (Laid-Open) No. 59242/1989].
These processes comprise adding to a polymerizable monomer a coloring substance (e.g. carbon black) and other additives (e.g. dispersing agent) and then conducting emulsion or suspension polymerization to produce a coloring agent-containing toner by one-stage polymerization.
In these processes, however, the coloring agent is not uniformly dispersed in the polymer particles and the toner properties are not satisfactory.
Further, there were investigated a process which uses a grafted carbon black obtained by graft-polymerizing a monomer component in the presence of carbon black (DT Patent No. 3102823), a process which uses a carbon black surface-treated with a polymer having an oxazoline group, an aziridine group or the like [Japanese Patent Application Kokai (Laid-Open) No. 156760/1989], and a process which comprises polymerizing a monomer in the presence of carbon black and a polymer having compatibility with a functional group present on the surface of the carbon black or having a reactive group (e.g. amino group) reactive with said functional group [e.g. Japanese Patent Application Kokai (Laid-Open) No. 50450/1984, Japanese Patent Application Kokai (Laid-Open) No. 67563/1987]. In these processes, however, the type of carbon black used is restricted or the number of the steps is larger making the product quality non-uniform. The process which comprises conducting polymerization in the presence of a polar monomer and additives (e.g. stabilizer such as polyvinyl alcohol or the like), give no sufficient effect and the colored fine particles obtained have a problem in pigment dispersibility.
In recent years, recording in color has made and is still making a rapid progress. Hence, it is actively under way to develop colored fine particles wherein an organic coloring agent, in place of carbon black, is uniformly dispersed in polymer fine particles. Presently, however, there is no technique in which an organic coloring agent, similarly to an inorganic pigment, can be dispersed in a polymerizable monomer; development of a new technique is therefore necessary.
Hence, the objects of the present invention are to provide novel colored spherical fine particles comprising polymer fine particles and a coloring agent uniformly dispersed therein; a process for their production; and their applications.